Zoom lens

ABSTRACT

Provided is a zoom lens including four lens groups having refracting powers of negative, positive, negative and positive, respectively, arranged in the mentioned order from the objective side of the zoom lens, wherein, upon zooming from a short forcal length to a long forcal length, a first lens group moves at first toward the image side and then is reversed to move toward the objective side, while second, third and fourth lens groups all monotonously move toward the objective side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens, and particularly to a zoomlens having a picture angle reaching up to 84 deg. at its wide angleend, and a variable power ratio amounted to about 3, preferably used asan interchangeable lens for a single-lens reflex camera of 35 mm size.

2. Description of the Prior Art

Recently, the picture angle, to be covered, of zoom lenses used asinterchangeable lenses for a 35 mm size still camera is more and morelarge. There may be found two trends in such a kind of zoom lenses.

One of these trends is to increase the variable power ratio of the zoomlens even through the picture angle there of becomes more or less smallso that the zoom lens has 28 mm at its wide angle end and a variablepower ratio of 3. A zoom lens of this type is disclosed in, for example,Japanese Patent Publication No. 14403/80.

The other of the trends is to provide a zoom lens which has a super-wideangle amounted to 24 mm at its wind angle end even though its variablepower ratio is small such as, for example, about 2. Zoom lens of such akind are disclosed in, for example, Japanese Patent Laid-OpenPublication No. 118213/82 and Japanese Patent Laid-Open Publication No.26816/82.

However, in the former zoom lens, if the zoom lens is shifted to thewide angle side while its zoom ratio is maintained, the amounts ofaberrations generated in an obliquely incident light beam, such as, forexample, astigmatism and chromatic aberration of magnification inparticular, are made large so that a high performance cannot be obtainedon the short focal length side, and as well the space between the firstand second lens groups becomes large, causing an increase in thediameter of the front lens or a decrease in the brighthess of the edgesof the image field.

Meanwhile, in the latter zoom lens, if its zooming range is extended tothe telescopic side to increase its zoom ratio, aberration due to anincrease in the lens diameter, such as, for example, sphericalaberration, color-offset due to spherical aberration, and coma inparticular become large. Further, the zoom lens inevitably has a largesize since the moving distance of the variator is large, and as well,the operationability of the zoom lens is made deteriorate.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a zoom lens which isimproved of the afore-mentioned well-known zoom lens while still havingthe advantages of the same, thereby the zoom lens according to thepresent invention has a super-wide angle and a large variable powerratio which are beyond those of conventional zoom lenses, and as well iscompact and well-compensated in aberrations.

According to the present invention, there is provided a zoom lens, whichhas an arrangement and a moving locus diagram as shown in FIGS. 1 and 2,including a first lens group (I) having a negative refractive power, asecond lens group (II) having a positive refractive power, a third lensgroup (III) having a negative refractive power and a fourth lens group(IV) having a positive refractive power, which are arranged in thementioned order from the objective side of the zoom lens, wherein, uponzooming from the short focal length side to the long focal length side,the first-lens group (I) moves at first to the image side and then isreversed to move toward the objective side, while the second, third andfourth lens groups monotonously move toward the objective side bydifferent distances, respectively, and further the following conditionsare satisfied: ##EQU1## where f_(w) : shortest focal length;

f_(i) : focal length of i-th lens group;

l_(i) : moving distance of i-th lens group;

r₂₀, r₂₁ : radii of curvature of objective and image side surfaces ofair lens in third lens group:

r₂₆ : radius of curvature of joint surface in fourth lens group; and

n₁₄, n₁₅ : refractive indexes of lens materials on both sides of jointsurface in fourth lens group, with respect to d-ray.

Among the above-mentioned conditions, the condition (1) gives therefractive power of the first lens group which acts as a compensator formaintaining a constant image position during zooming, and dominates notonly the aberration compensation of the zoom lens but also the importantcharacteristics of the zoom lens, such as, for example, compactness, theshape of curve of a cam, the feed amount of lenses, the brightness ofthe edges of the image field, etc., thereby the condition (1) has animportant factor which is not too much said that it determines theskeleton of the zoom lens.

If the refractive power becomes high in excess of the lower limit ofthis condition, the generation of coma is made large in the rangebetween the intermediate focal length and the long focal length.Further, it is resulted in an excessive compensation of sphericalaberration on the long focal lenth side.

On the contrary, if the refractive power becomes weak in excess of theupper limit of this condition, the space between the first and secondlens groups is made large at the end of the short focal length so thatthe gradient of the cam is steep since the feed amount of lenses shouldbe made large, thereby not only the operationability of the zoom lensdeteriorates, but also the diameter of the front lens cannot be easilymade small, resulting in lowering of the brightness of the edge of theimage field.

The condition (2) is to make the refractive power of the second lensgroup as a main variator appropriate for reconciling the compensation ofaberration and a high variable power ratio.

If the lower limit is exceeded, fluctuations in spherical aberration dueto zooming of the lens cannot be eliminated so that spherical aberrationdue to insufficient compensation firmly remains in the intermediaterange of focal length. On the contrary, if the upper limit is exceeded,the effect of variable power decreases, and therefore, the zoom lenscannot have a high zooming magnification. Further, a necessary movingdistance becomes large so that a compact zoom lens is not obtainable.

The condition (3) gives the refractive power of the third lens group.The third lens group makes spherical aberration appropriate on the shortfocal length side in cooperation with the fourth lens group. If thelower limit is exceeded, the spherical aberration in this range issubjected to excessive compensation. If this is compensated by thefourth lens group, coma is generated over all zooming range. On thecontrary, if the upper limit is exceeded, such an effect that thearrangement of the lens system becomes a telescopic type is reduced onthe long focal length side, resulting in making the lens system large.

The condition (4) relates to the divergent action of the air lens formedin the third group. If the lower limit is exceeded, the refractive powerof this air lens becomes excessively weak, and therefore, it isnecessary to allot the refractive power to the other specific surfaces.As a result, the concentration of refractive power to the specificsurfaces may arise so that large variations in the picture angle of asagittal image surface come about on the short focal length side, whichbecomes rapidly excessive at the periphery of the image surface. On thecontrary, if the upper limit is exceeded, the sine condition tends toshift toward the negative side, and therefore, the compensation of comais made difficult.

The condition (5) relates to the refractive power of the joint surfacesincluded in the fourth lens group. By utilizing such a phenomenon that alight beam directed to the image surface becomes narrow in this surface,the generation of coma is restrained to maintain the image surface atits appropriate position. If the upper limit is exceeded, the generationof coma due to the divergency of the light passing through theperipheral edge part of this image surface is made large. On thecontrary, if the lower limit is exceeded, the effect of image surfacecompensation is insufficient, which is particularly remarkable on theshort focal length side. Further, distortion excessively varies uponzooming.

The condition (6) gives the moving distances of the second, third andfourth lens group. Since the angle of the light which emanates from thethird lens group and is incident to the fourth lens group and which hasa large image angle, is large with respect to the optical axis on theshort focal length side, if the space between the first and fourth lensgroups is made large, astigmatism increasse, and therefore, the diameterof the rear lens also increases. Therefore, the condition of l₂ >l₄ isnecessary.

Further, in order to obtain a compact zoom lens, a large refractivepower is allotted to each lens group. It is liable to generate thedistortion of spool type on the long focal length side due to thestrongest refractive power of the third lens group. On the contrary, theinclined angle of the main light ray in the third lens group can be madesmall by moving the third lens group so as to be positioned away fromthe image surface, and therefore, distorsion can be reduced. However,since this movement is in the direction in which the variable power ismade small, it is not advisable to make this large. Therefore, thecondition of l₄ >l₃, l₃ >0 is necessary.

Finally, is obtained the following:

    0<l.sub.3 <l.sub.4 <l.sub.2,

and therefore,

    0<l.sub.3 /l.sub.2 <l.sub.4 /l.sub.2 <1.

The zoom lens which satisfies the above-mentioned conditions preferablehas a first lens group composed of a negative meniscus single lens L₁having its convex surface directed to the objective side, a positivesingle lens L₂, a negative meniscus single lens L₃ having its convexsurface directed to the objective side and a jointed lens in which adouble-concave lens L₄ and a positive meniscus single lens L₅ having itsconvex surface directed to the objective side are jointed together,those lenses being arranged in the mentioned order from the objectiveside. The arrangement of the first lens group corresponds to, incomparison with that disclosed in the Japanese Patent Laid-OpenPublication No. 118213/82, the jointed lens consisting of the fourthlens L₄ and the fifth lens L₅ which are jointed together. With thisarrangement the position of the principal point of the first lens groupis advantageous.

The concave lens L₁ decrease the inclined angle of peripheral light beamwhich impinges thereto at a large angle, and then makes the light beamimpinge to the positive lens L₂ so that the chromatic aberration ofmanginfication which hinders the realization of wideangle is reduced.

Further, concerning the second and third lens groups, the second lensgroup is composed preferably of a positive single lens L₆, a jointedlens consisting of a negative meniscus lens L₇ having a convex surfacedirected to the objective side and a positive lens L₈ jointed together,and a positive single lens L₉, those lenses being arranged in thementioned order from the objective side, and the third lens group issimilarly composed preferably of a jointed lens consisting of a positivemeniscus lens L₁₀ having its convex surface directed to the image sideand a double-concave lens L₁₁ which are jointed together, and a negativesingle lens L₁₂.

In the above-mentioned type of zoom lenses, the difference in sphericalaberration by colors is liable to generate on the long focal lengthside. The difference by colors is generated, due to excessivecompensation, in the second lens group in which the light beam is madewidest, and the spherical aberration by under-colors is generated in thejointed surfaces in the first and third lens groups, thereby thespherical aberration by colors in the total optical system can besatisfactorily compensated.

Further, in this arrangement of lenses all joint surfaces are disposedconcentrically with a diaphragm which is positioned between the secondand third lens groups so that the generation of differences in thecurvature of field and coma by colors is made extremely small, andtherefore, a zoom lens whose chromatic aberration is satisfactorilycompensated can be obtained.

In this type of zoom lenses, the zoom lenses which is possible to beused for macro-photography, are widely available these days. It ispreferable that the macro-photography is set on from the short focallength side. In the arrangement of the zoom lens according to thepresent invention, it is most advantageous to move the second or fourthlens group toward the objective side from the short focal length side inaccordance with the condition (6). At this stage, although the firstlens group is stationary, if the feed of lenses for short-distancephotography is superposed to the above-mentioned function, thephotography of maximum magnification can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagram of moving locus of a zoom lens according tothe present invention;

FIG. 2 illustrates a view for the arrangement of lenses having anintermediate focal length in the first embodiment of the presentinvention;

FIGS. 3 through 6 shows aberration diagrams in the first to fourthembodiments, respectively, in which (A), (B) and (C) indicate in thecases of short, intermediate and long focal lengths, respectively; and

FIG. 7 shows an aberration diagram in the first embodiment uponmacro-photography.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments according to the present invention which satisfy all of theabove-mentioned conditions will be explained hereinbelow:

In the tables numeral d_(i) denotes a spacial distance between i-th andi+1-th refractive surfaces as viewed from the objective side along theoptical axis, ν_(i) similarly denotes the abbe's number of the materialof i-th lens with respect to d-ray.

    ______________________________________                                        First Embodiment                                                              ______________________________________                                        25.7 < f < 73 F.sub.NO = 4                                                                  Aberration Diagram in FIG. 3                                    83.2° > 2ω > 32°                                          r.sub.1 = 94.156                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.67003                                                                         ν.sub.1 = 47.2                          r.sub.2 = 33.236                                                                         d.sub.2 = 7.8                                                      r.sub.3 = 220.768                                                                        d.sub.3 = 4.4                                                                             n.sub.2 = 1.75500                                                                         ν.sub.2 = 52.33                         r.sub.4 = -128.656                                                                       d.sub.4 = .1                                                       r.sub.5 = 99.691                                                                         d.sub.5 = 1.4                                                                             n.sub.3 = 1.69680                                                                         ν.sub.3 = 55.46                         r.sub.6 = 45.897                                                                         d.sub.6 = 4.7                                                      r.sub.7 = -110.865                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.75500                                                                         ν.sub.4 = 52.33                         r.sub.8 = 25.117                                                                         d.sub.8 =  5.5                                                                            n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.83                         r.sub.9 = 78.553                                                                         d.sub.9 = variable                                                 r.sub.10 = 99.482                                                                        d.sub.10 = 2.3                                                                            n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -161.832                                                                      d.sub.11 = .1                                                      r.sub.12 = 76.169                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 20.565                                                                        d.sub.13 = 5.0                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = 445.917                                                                       d.sub.14 = .1                                                      r.sub.15 = 29.76                                                                         d.sub.15 = 3.7                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -364.194                                                                      d.sub.16 = variable                                                r.sub.17 = -83.25                                                                        d.sub.17 = 1.8                                                                            n.sub.10 = 1.84666                                                                        ν.sub.10 = 23.83                        r.sub.18 = -25.292                                                                       d.sub.18 = .9                                                                             n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 57.893                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -32.375                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.69680                                                                        ν.sub.12 = 55.46                        r.sub.21 = 435.585                                                                       d.sub.21 = variable                                                r.sub.22 = -235.012                                                                      d.sub.22 = 3.1                                                                            n.sub.13 = 1.69680                                                                        ν.sub.13 = 55.46                        r.sub.23 = -24.932                                                                       d.sub.23 = .1                                                      r.sub.24 = 121.076                                                                       d.sub.24 = 7.5                                                                            n.sub.14 =1.58913                                                                         ν.sub.14 = 61.25                        r.sub.25 = -15.903                                                                       d.sub.25 = 1.0                                                                            n.sub.15 =1.83400                                                                         ν.sub.15 = 37.34                        r.sub.26 = -58.017                                                            ______________________________________                                        Variable Space Distance                                                       f          25.7    43.314         73                                          ______________________________________                                        d.sub.9    31.908  12.109         1.221                                       d.sub.16    4.542  10.517         19.425                                      d.sub.21    8.969   5.856         1.528                                       ______________________________________                                    

The amounts of the conditional formula

(i) 1.362

(ii) 1.043

(iii) 0.943

(iv) 1.156

(v) 0.531

(vi) 0<0.35<0.675<1

In order to carry out macro-photography with the use of this zoom lens,the second, third and fourth lens groups are moved from the shortestfocal length by the following distances:

the seconds lens group: 4.004

the third lens group: 1.43

the fourth lens group: 3.028

Thereby, an object positioned at 262 mm from the film surface can bephotographed on a reduction rate of -1/4.9×. The aberration diagram atthis stage is shown in FIG. 7(A).

Further, the condition (6) is well-satisfied since:

    0<l.sub.3 /l.sub.2 (=0.35)<l.sub.4 /l.sub.2 (=0.741)<1.

When the distance of close range photography is set to 0.8 mm in normalphotography, it is necessary to feed out the first lens group by anamount of 1.747 mm to focus therefor. If this feed amount is superposedto the lens movement for macro-photography, an object positioned at 232mm in the close range can be photographed on a reduction rate of-1/3.97×. The aberration diagram at this stage is shown in FIG. 7(A).

    ______________________________________                                        Second Embodiment                                                             ______________________________________                                        24.8 ≦ f ≦ 70                                                                 F.sub.NO = 4                                                    85.4° > 2ω > 33.2°                                                      Aberration Diagram in FIG. 4                                    r.sub.1 = 90.049                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.66672                                                                         ν.sub.1 = 48.30                         r.sub.2 = 33.900                                                                         d.sub.2 = 7.6                                                      r.sub.3 = 218.528                                                                        d.sub.3 = 4.5                                                                             n.sub.2 = 1.71300                                                                         ν.sub.2 = 53.94                         r.sub.4 = -144.319                                                                       d.sub.4 = .1                                                       r.sub.5 = 102.913                                                                        d.sub.5 = 1.4                                                                             n.sub.3 = 1.64000                                                                         ν.sub.3 = 60.15                         r.sub.6 = 41.332                                                                         d.sub.6 = 5.0                                                      r.sub.7 = -149.196                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.75500                                                                         ν.sub.4 = 52.33                         r.sub.8 = 25.242                                                                         d.sub.8 =  5.5                                                                            n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.83                         r.sub.9 = 73.930                                                                         d.sub.9 = variable                                                 r.sub.10 = 99.221                                                                        d.sub.10 = 2.3                                                                            n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -176.043                                                                      d.sub.11 = .1                                                      r.sub.12 = 98.353                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 22.340                                                                        d.sub.13 = 5.0                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = -2907.673                                                                     d.sub.14 = .1                                                      r.sub.15 = 29.376                                                                        d.sub.15 = 3.7                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -380.375                                                                      d.sub.16 = variable                                                r.sub.17 = -76.959                                                                       d.sub.17 = 1.9                                                                            n.sub.10 = 1.84666                                                                        ν.sub.10 = 23.83                        r.sub.18 = -26.088                                                                       d.sub.18 = .9                                                                             n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 86.694                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -34.298                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.69680                                                                        ν.sub.12 = 55.46                        r.sub.21 = 144.605                                                                       d.sub.21 = variable                                                r.sub.22 = -228.816                                                                      d.sub.22 = 3.0                                                                            n.sub.13 = 1.69680                                                                        ν.sub.13 = 55.46                        r.sub.23 = -24.460                                                                       d.sub.23 = .1                                                      r.sub.24 = 126.483                                                                       d.sub.24 = 7.2                                                                            n.sub.14 = 1.58913                                                                        ν.sub.14 = 61.25                        r.sub.25 = -15.949                                                                       d.sub.25 = 1.1                                                                            n.sub.15 = 1.83400                                                                        ν.sub.15 = 37.34                        r.sub.26 = -57.092                                                            ______________________________________                                        Variable Space Distance                                                       f          24.8    41.665         70                                          ______________________________________                                        d.sub.9    30.884  11.715         1.208                                       d.sub.16   4.002   10.287         19.613                                      d.sub.21   9.33     6.092         1.525                                       ______________________________________                                    

The amounts of the conditional formula

(i) 1.389

(ii) 1.089

(iii) 0.994

(iv) 1.003

(v) 0.521

(vi) 0<0.3<0.65<1

    ______________________________________                                        Third Embodiment                                                              ______________________________________                                        24.8 ≦ f ≦ 72.8                                                               F.sub.NO = 4                                                    85.4° ≧ 2ω ≧ 32.2°                                        Aberration Diagram in FIG. 5                                    r.sub.1 = 95.222                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.66672                                                                         ν.sub.1 = 48.30                         r.sub.2 = 35.025                                                                         d.sub.2 = 7.6                                                      r.sub.3 = 188.753                                                                        d.sub.3 = 4.5                                                                             n.sub.2 = 1.69680                                                                         ν.sub.2 = 55.46                         r.sub.4 = -147.207                                                                       d.sub.4 = .1                                                       r.sub.5 = 105.648                                                                        d.sub.5 = 1.4                                                                             n.sub.3 = 1.62041                                                                         ν.sub.3 = 60 34                         r.sub.6 = 40.548                                                                         d.sub.6 = 5.1                                                      r.sub.7 = -191.182                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.75500                                                                         ν.sub.4 = 52.33                         r.sub.8 = 24.566                                                                         d.sub.8  = 5.5                                                                            n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.83                         r.sub.9 = 66.528                                                                         d.sub.9 = variable                                                 r.sub.10 = 86.785                                                                        d.sub.10 = 2.3                                                                            n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -311.359                                                                      d.sub.11 = .1                                                      r.sub.12 = 78.584                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 21.564                                                                        d.sub.13 = 5.0                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = 541.895                                                                       d.sub.14 = .1                                                      r.sub.15 = 29.638                                                                        d.sub.15 = 3.7                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -436.795                                                                      d.sub.16 = variable                                                r.sub.17 = -103.359                                                                      d.sub.17 = 1.9                                                                            n.sub.10 = 1.84666                                                                        ν.sub.10 =  23.83                       r.sub.18 = -28.864                                                                       d.sub.18 = .9                                                                             n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 62.037                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -31.025                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.71300                                                                        ν.sub.12 = 53.94                        r.sub.21 = 1800.352                                                                      d.sub.21 = variable                                                r.sub.22 = -157.739                                                                      d.sub.22 = 3.0                                                                            n.sub.13 = 1.71300                                                                        ν.sub.13 = 53.94                        r.sub.23 = -24.981                                                                       d.sub.23 = .1                                                      r.sub.24 = 104.923                                                                       d.sub.24 = 7.2                                                                            n.sub.14 = 1.58913                                                                        ν.sub.14 = 61.25                        r.sub.25 = -16.230                                                                       d.sub.25 = 1.1                                                                            n.sub.15 = 1.83400                                                                        ν.sub.15 = 37.34                        r.sub.26 = -57.580                                                            ______________________________________                                        Variable Space Distance                                                       f          24.8    42.49          72.8                                        ______________________________________                                        d.sub.9    31.949  12.018         1.433                                       d.sub.16   3.708   9.876          19.311                                      d.sub.21   9.259   5.946          1.457                                       ______________________________________                                    

The amounts of the conditional formula

(i) 1.401

(ii) 1.111

(iii) 1.109

(iv) 1.222

(v) 0.516

(vi) 0<0.4<0.7<1.0

    ______________________________________                                        Fourth Embodiment                                                             ______________________________________                                        25.7 ≦ f ≦ 73                                                                 F.sub.NO = 4                                                    83.4° > 2ω > 31.8°                                                      Aberration Diagram in FIG. 6                                    r.sub.1 = 84.928                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.67003                                                                         ν.sub.1 = 47.20                         r.sub.2 = 31.837                                                                         d.sub.2 = 8.1                                                      r.sub.3 = 256.904                                                                        d.sub.3 = 4.2                                                                             n.sub.2 = 1.71300                                                                         ν.sub.2 = 53.94                         r.sub.4 = -127.262                                                                       d.sub.4 = .1                                                       r.sub.5 = 113.601                                                                        d.sub.5 = 1.4                                                                             n.sub.3 = 1.62041                                                                         ν.sub.3 = 60.34                         r.sub.6 = 49.737                                                                         d.sub.6 = 4.6                                                      r.sub.7 = -131.053                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.71300                                                                         ν.sub.4 = 53.94                         r.sub.8 = 22.236                                                                         d.sub.8 =  6.0                                                                            n.sub.5 = 1.80518                                                                         ν.sub.5 = 25.46                         r.sub.9 = 63.486                                                                         d.sub.9 = variable                                                 r.sub.10 = 96.464                                                                        d.sub.10 =0 2.3                                                                           n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -167.838                                                                      d.sub.11 = .1                                                      r.sub.12 = 63.858                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 20.058                                                                        d.sub.13 = 5.2                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = 196.304                                                                       d.sub.14 = .1                                                      r.sub.15 = 30.338                                                                        d.sub.15 = 3.9                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -274.039                                                                      d.sub.16 = variable                                                r.sub.17 = -71.458                                                                       d.sub.17 = 2.1                                                                            n.sub.10 = 1.80518                                                                        ν.sub.10 = 25.46                        r.sub.18 = -22.061                                                                       d.sub.18 = .9                                                                             n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 65.142                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -35.803                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.69680                                                                        ν.sub.12 = 55.46                        r.sub.21 = 259.242                                                                       d.sub.21 = variable                                                r.sub.22 = -294.242                                                                      d.sub.22 = 3.1                                                                            n.sub.13 = 1.69680                                                                        ν.sub.13 = 55.46                        r.sub.23 = -25.251                                                                       d.sub.23 = .1                                                      r.sub.24 = 165.577                                                                       d.sub.24 = 7.0                                                                            n.sub.14 = 1.58913                                                                        ν.sub.14 = 61.25                        r.sub.25 = -15.718                                                                       d.sub.25 = 1.0                                                                            n.sub.15 = 1.83400                                                                        ν.sub.15 = 37.34                        r.sub.26 = -52.669                                                            ______________________________________                                        Variable Space Distance                                                       f          25.7    43.314         73                                          ______________________________________                                        d.sub.9    31.928  12.154         1.242                                       d.sub.16   4.16    10.107         19.043                                      d.sub.21    8.635  5.47           1.194                                       ______________________________________                                    

The amounts of the conditional formula

(i) 1.362

(ii) 1.042

(iii) 0.934

(iv) 1.039

(v) 0.537

(vi) 0<0.35<0.675<1.0

What is claimed is:
 1. A zoom lens including a first lens group having anegative refractive power, a second lens group having a positiverefractive power, a third lens group having a negative refractive powerand a fourth lens group having a positive refractive power, which arearranged in the mentioned order from the objective side of the zoomlens, said third lens group having therein an air lens, and said fourthlens group having therein at least one joint surface, wherein uponzooming from the short focal length side to the long focal length side,said first-lens group moves at first to the image side and then isreversed to move toward the objective side, while said second, third andfourth lens group monotonously move toward the objective side bydifferent distances, respectively, and further the following conditionsare satisfied: ##EQU2## where f₂ : shortest focal length;f_(i) : focallength of i-th lens group; l_(i) : moving distance of i-th lens groupupon zooming; r₂₀, r₂₁ : radii of curvature of objective and image sidesurfaces of air lens in third lens group: r₂₆ : radius of curvature ofjoint surface in fourth lens group; and n₁₄, n₁₅ : refractive indexes oflens materials on both sides of joint surface in fourth lens group, withrespect to d-ray.
 2. A zoom lens as set forth in claim 1, wherein saidfirst lens group comprises a negative meniscus single lens having itsconvex surface directed to the objective side, a positive single lens, anegative meniscus single lens having its convex surface directed to theobjective side and a jointed lens including a double-concave lens and apositive meniscus lens having its convex surface directed to theobjective side which are jointed together, said those lenses beingarranged in the mentioned order from the objective side.
 3. A zoom lensas set forth in claim 1 or 2, wherein said second lens group comprises apositive single lens, a jointed lens including a negative meniscus lenshaving its convex surface directed to the objective side and a positivelens which are jointed together, and a positive single lens, said thoselens being arranged in the mentioned order from the objective side, andsaid third lens group comprises a jointed lens including a positivemeniscus lens having its convex surface directed to the image side and adouble-concave single lens which are jointed together, and a negativesingle lens.
 4. A zoom lens as set forth in claim 1, or 2, wherein saidsecond, and third and fourth lens groups can be moved toward theobjective side in accordance with the following conditions:

    0<l.sub.3 /l.sub.2 <l.sub.4 /l.sub.2 <1

thereby, macro-photography can be made.
 5. A zoom lens as set forth inclaim 1 as shown by the following data:

    ______________________________________                                                25.7 < f < 73                                                                            F.sub.NO = 4                                                       83.2° > 2ω > 32°                                  r.sub.1 = 94.156                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.67003                                                                         ν.sub.1 = 47.2                          r.sub.2 = 33.236                                                                         d.sub.2 = 7.8                                                      r.sub.3 = 220.768                                                                        d.sub.3 = 4.4                                                                             n.sub.2 = 1.75500                                                                         ν.sub.2 = 52.33                         r.sub.4 = -128.656                                                                       d.sub.4 = .1                                                       r.sub.5 = 99.691                                                                         d.sub.5 = 1.4                                                                             n.sub.3 = 1.69680                                                                         ν.sub.3 = 55.46                         r.sub.6 = 45.897                                                                         d.sub.6 = 4.7                                                      r.sub.7 = -110.865                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.75500                                                                         ν.sub.4 = 52.33                         r.sub.8 = 25.117                                                                         d.sub.8 = 5.5                                                                             n.sub.5 = 1.84666                                                                         ν .sub.5 = 23.83                        r.sub.9 = 78.553                                                                         d.sub.9 = variable                                                 r.sub.10 = 99.482                                                                        d.sub.10 =2.3                                                                             n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -161.832                                                                      d.sub.11 = .1                                                      r.sub.12 = 76.169                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 20.565                                                                        d.sub.13 = 5.0                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = 445.917                                                                       d.sub.14 = .1                                                      r.sub.15 = 29.76                                                                         d.sub.15 = 3.7                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -364.194                                                                      d.sub.16 = variable                                                r.sub.17 = -83.25                                                                        d.sub.17 = 1.8                                                                            n.sub.10 = 1.84666                                                                        ν.sub.10 = 23.83                        r.sub.18 = -25.292                                                                       d.sub.18  = .9                                                                            n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 57.893                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -32.375                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.69680                                                                        ν.sub.12 = 55.46                        r.sub.21 = 435.585                                                                       d.sub.21 = variable                                                r.sub.22 = -235.012                                                                      d.sub.22 = 3.1                                                                            n.sub.13 = 1.69680                                                                        ν.sub.13 = 55.46                        r.sub.23 = -24.932                                                                       d.sub.23 = .1                                                      r.sub.24 = 121.076                                                                       d.sub.24 = 7.5                                                                            n.sub.14 = 1.58913                                                                        ν.sub.14 = 61.25                        r.sub.25 = -15.903                                                                       d.sub.25 = 1.0                                                                            n.sub.15 = 1.83400                                                                        ν.sub.15 = 37.34                        r.sub.26 = -58.017                                                            ______________________________________                                        Variable space distance:                                                      f          25.7    43.314         73                                          ______________________________________                                        d.sub.9    31.908  12.109         1.221                                       d.sub.16   4.542   10.517         19.425                                      d.sub.21   8.969    5.856         1.528                                       ______________________________________                                    

where f: synthetic focal length of total system w: half image angle r:radius of curvature of refractive surface d: space distance betweenrefractive surfaces n: refractive index ν: abbe's number.
 6. A zoom lensas set forth in claim 5, wherein said second, third and fourth lensgroups are moved respectively bysaid second lens: 4.084 said third lens:1.43 said fourth lens: 3.028thereby macro-photography is made.
 7. A zoomlens as set forth in claim 1 as shown by the following data:

    ______________________________________                                                24.8 ≦ f ≦ 70                                                              F.sub.NO = 4                                                       85.4° > 2ω > 33.2°                                r.sub.1 = 90.049                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.66672                                                                         ν.sub.1 = 48.30                         r.sub.2 = 33.900                                                                         d.sub.2 = 7.6                                                      r.sub.3 = 218.528                                                                        d.sub.3 = 4.5                                                                             n.sub.2 = 1.71300                                                                         ν.sub.2 = 53.94                         r.sub.4 = -144.319                                                                       d.sub.4 = .1                                                       r.sub.5 = 102.913                                                                        d.sub.5 = 1.4                                                                             n.sub.3 = 1.64000                                                                         ν.sub.3 = 60.15                         r.sub.6 = 41.332                                                                         d.sub.6 = 5.0                                                      r.sub.7 = -149.196                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.75500                                                                         ν.sub.4 = 52.33                         r.sub.8 = 25.242                                                                         d.sub.8 = 5.5                                                                             n.sub.5 = 1.84666                                                                         ν .sub.5 = 23.83                        r.sub.9 = 73.930                                                                         d.sub.9 = variable                                                 r.sub.10 = 99.221                                                                        d.sub.10 = 2.3                                                                            n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -176.043                                                                      d.sub.11 = .1                                                      r.sub.12 = 98.353                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 22.340                                                                        d.sub.13 = 5.0                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = -2907.673                                                                     d.sub.14 = .1                                                      r.sub.15 = 29.376                                                                        d.sub.15 = 3.7                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -380.375                                                                      d.sub.16 = variable                                                r.sub.17 = -76.959                                                                       d.sub.17 = 1.9                                                                            n.sub.10 = 1.84666                                                                        ν.sub.10 = 23.83                        r.sub.18 = -26.088                                                                       d.sub.18 = .9                                                                             n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 86.694                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -34.298                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.69680                                                                        ν.sub.12 = 55.46                        r.sub.21 = 144.605                                                                       d.sub.21 = variable                                                r.sub.22 = -228.816                                                                      d.sub.22 = 3.0                                                                            n.sub.13 = 1.69680                                                                        ν.sub.13 = 55.46                        r.sub.23 = -24.460                                                                       d.sub.23 = .1                                                      r.sub.24 = 126.483                                                                       d.sub.24 = 7.2                                                                            n.sub.14 = 1.58913                                                                        ν.sub.14 = 61.25                        r.sub.25 = -15.949                                                                       d.sub.25 = 1.1                                                                            n.sub.15 = 1.83400                                                                        ν.sub.15 = 37.34                        r.sub.26 = -57.092                                                            ______________________________________                                        Variable space distance                                                       f          24.8    41.665         70                                          ______________________________________                                        d.sub.9    30.884  11.715         1.208                                       d.sub.16   4.002   10.287         19.613                                      d.sub.21   9.33     6.092         1.525                                       ______________________________________                                    


8. A zoom lens as set forth in claim 1 as shown by the following data;

    ______________________________________                                                24.8 ≦ f ≦ 72.8                                                            F.sub.NO = 4                                                       85.4° ≧ 2ω ≧ 32.2°                  r.sub.1 = 95.222                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.66672                                                                         ν.sub.1 = 48.30                         r.sub.2 = 35.025                                                                         d.sub.2 = 7.6                                                      r.sub.3 = 188.753                                                                        d.sub.3 = 4.5                                                                             n.sub.2 = 1.69680                                                                         ν.sub.2 = 55.46                         r.sub.4 = -147.207                                                                       d.sub.4 = .1                                                       r.sub.5 = 105.648                                                                        d.sub.5 = 1.4                                                                             n.sub.3 = 1.62041                                                                         ν.sub.3 = 60.34                         r.sub.6 = 40.548                                                                         d.sub.6 = 5.1                                                      r.sub.7 = -191.182                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.75500                                                                         ν.sub.4 = 52.33                         r.sub.8 = 24.566                                                                         d.sub.8 = 5.5                                                                             n.sub.5 = 1.84666                                                                         ν .sub.5 = 23.83                        r.sub.9 = 66.528                                                                         d.sub.9 = variable                                                 r.sub.10 = 86.785                                                                        d.sub.10 = 2.3                                                                            n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -311.359                                                                      d.sub.11 = .1                                                      r.sub.12 = 78.584                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 21.564                                                                        d.sub.13 = 5.0                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = 541.895                                                                       d.sub.14 = .1                                                      r.sub.15 = 29.638                                                                        d.sub.15 = 3.7                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -436.795                                                                      d.sub.16 = variable                                                r.sub.17 = -103.359                                                                      d.sub.17 = 1.9                                                                            n.sub.10 = 1.84666                                                                        ν.sub.10 = 23.83                        r.sub.18 = -288.864                                                                      d.sub. 18 = .9                                                                            n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 62.037                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -31.025                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.71300                                                                        ν.sub.12 = 53.94                        r.sub.21 = 1800.352                                                                      d.sub.21 = variable                                                r.sub.22 = -157.739                                                                      d.sub.22 = 3.0                                                                            n.sub.13 = 1.71300                                                                        ν.sub.13 = 53.94                        r.sub.23 = -24.981                                                                       d.sub.23 = .1                                                      r.sub.24 = 104.923                                                                       d.sub.24 = 7.2                                                                            n.sub.14 = 1.58913                                                                        ν.sub.14 = 61.25                        r.sub.25 = -16.230                                                                       d.sub.25 = 1.1                                                                            n.sub.15 = 1.83400                                                                        ν.sub.15 = 37.34                        r.sub.26 = -57.580                                                            ______________________________________                                        Variable space distance                                                       f          24.8    42.49          72.8                                        ______________________________________                                        d.sub.9    31.949  12.018         1.433                                       d.sub.16   3.708   9.876          19.311                                      d.sub.21   9.259   5.946          1.457                                       ______________________________________                                    


9. A zoom lens as set forth in claim 1 as shown by the following data:

    ______________________________________                                                25.7 ≦ f ≦ 73                                                              F.sub.NO = 4                                                       83.4° > 2ω > 31.8°                                r.sub.1 = 84.928                                                                         d.sub.1 = 1.6                                                                             n.sub.1 = 1.67003                                                                         ν.sub.1 = 47.20                         r.sub.2 = 31.837                                                                         d.sub.2 = 8.1                                                      r.sub.3 = 256.904                                                                        d.sub.3 = 4.2                                                                             n.sub.2 = 1.71300                                                                         ν.sub.2 = 53.94                         r.sub.4 = -127.262                                                                       d.sub.4 = .1                                                       r.sub.5 = 113.601                                                                        d.sub.5 = 1.4                                                                             n.sub.3 = 1.62041                                                                         ν.sub.3 = 60.34                         r.sub.6 = 49.737                                                                         d.sub.6 = 4.6                                                      r.sub.7 = -131.053                                                                       d.sub.7 = 1.3                                                                             n.sub.4 = 1.71300                                                                         ν.sub.4 = 53.94                         r.sub.8 = 22.236                                                                         d.sub.8 = 6.0                                                                             n.sub.5 = 1.80518                                                                         ν .sub.5 = 25.46                        r.sub.9 = 63.486                                                                         d.sub.9 = variable                                                 r.sub.10 = 96.464                                                                        d.sub.10 = 2.3                                                                            n.sub.6 = 1.71300                                                                         ν.sub.6 = 53.94                         r.sub.11 = -167.838                                                                      d.sub.11 = .1                                                      r.sub.12 = 63.858                                                                        d.sub.12 = .9                                                                             n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.83                         r.sub.13 = 20.058                                                                        d.sub.13 = 5.2                                                                            n.sub.8 = 1.75500                                                                         ν.sub.8 = 52.33                         r.sub.14 = 196.304                                                                       d.sub.14 = .1                                                      r.sub.15 = 30.338                                                                        d.sub.15 = 3.9                                                                            n.sub.9 = 1.62041                                                                         ν.sub.9 = 60.34                         r.sub.16 = -274.039                                                                      d.sub.16 = variable                                                r.sub.17 = -71.458                                                                       d.sub.17 = 2.1                                                                            n.sub.10 = 1.80518                                                                        ν.sub.10 = 25.46                        r.sub.18 = -22.061                                                                       d.sub. 18 = .9                                                                            n.sub.11 = 1.71300                                                                        ν.sub.11 = 53.94                        r.sub.19 = 65.142                                                                        d.sub.19 = 2.3                                                     r.sub.20 = -35.803                                                                       d.sub.20 = .9                                                                             n.sub.12 = 1.69680                                                                        ν.sub.12 = 55.46                        r.sub.21 = 259.242                                                                       d.sub.21 = variable                                                r.sub.22 = -294.242                                                                      d.sub.22 = 3.1                                                                            n.sub.13 = 1.69680                                                                        ν.sub.13 = 55.46                        r.sub.23 = -25.251                                                                       d.sub.23 = .1                                                      r.sub.24 = 165.577                                                                       d.sub.24 = 7.0                                                                            n.sub.14 = 1.58913                                                                        ν.sub.14 = 61.25                        r.sub.25 = -15.718                                                                       d.sub.25 = 1.0                                                                            n.sub.15 = 1.83400                                                                        ν.sub.15 = 37.34                        r.sub.26 = -52.669                                                            ______________________________________                                        Variable space distance                                                       f          25.7    43.314         73                                          ______________________________________                                        d.sub.9    31.928  12.154         1.242                                       d.sub.16   4.16    10.107         19.043                                      d.sub.21    8.635  5.47           1.194                                       ______________________________________                                    


10. A zoom lens as set forth in claim 3, wherein said second, third andfourth lens groups can be moved toward the objective side in accordancewith the following conditions:

    0<l.sub.3 /l.sub.2 <l.sub.4 /l.sub.2 <1

thereby, macro-photography can be made.